State of Subdivision

It might be noted that only for particles smaller than about 1 /ig or of surface area greater than a few square meters per gram does the surface energy become significant. Only for very small particles does the edge energy become important, at least with the assumption of perfect cubes. 

The numerical illustration given above is so highly idealized that any agreement with experiment could hardly be more than coincidental. A number of caveats have been mentioned, including the inadequacies of theoretical calculations, the various surface distortions and reconstructions expected, surface 

Variation of Specific Surface Eneigy with Particle Size  

Side (cm) Total Area (cm ) Total Edge (cm) Surface Energy (ergs/g) Edge Energy (ergs/g) 

Actual crystal planes tend to be incomplete and imperfect in many ways. Nonequilibrium surface stresses may be relieved by surface imperfections such as overgrowths, incomplete planes, steps, and dislocations (see below) as illustrated in Fig. VII-5 [98, 99]. The distribution of such features depends on the past history of the material, including the presence of adsorbing impurities [100]. Finally, for sufficiently small crystals (1-10 nm in dimension), quantum-mechanical effects may alter various physical (e.g., optical) properties [101]. 

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Vanadium pentoxide, vanadium(V) oxide, V2O5, is the most important compound in this oxidation state. It is a coloured solid (colour due to charge transfer, p. 60), the colour varying somewhat (red -> brown) with the state of subdivision it is formed when vanadium (or some of its compounds) is completely oxidised, and also by heating ammonium vanadate)V) ... 

Slurry Pipelines. Finely divided soHds can be transported in pipelines as slurries, using water or another stable Hquid as the suspending medium. Flow characteristics of slurries in pipelines depend on the state of subdivision of the soHds and their distribution within the fluid system. 

Nomenclature. Colloidal systems necessarily consist of at least two phases, the coUoid and the continuous medium or environment in which it resides, and their properties gready depend on the composition and stmcture of each phase. Therefore, it is useful to classify coUoids according to their states of subdivision and agglomeration, and with respect to the dispersing medium. The possible classifications of colloidal systems are given in Table 2. The variety of systems represented in this table underscores the idea that the problems associated with coUoids are usuaUy interdisciplinary in nature and that a broad scientific base is required to understand them completely. 

A study of how a sohd dries may be based on the internal mechanism of liquid flow or on the effec t of the external conditions of temperature, humidity, air flow, state of subdivision, etc., on the diying rate of the sohds. The former procedure generally requires a fundamental study of the internal condition. The latter procedure, although less fundamental, is more generally used because the results have greater immediate application in equipment design and evaluation. 

External Conditions The principal external variables involved in any drying study are temperature, humidity, air flow, state of subdivision of the solid, agitation of the solid, method of supporting the solid, and contact between hot surfaces and wet solid. Alf these variables will not necessarily occur in one problem. 

Uniformity of final moisture content Decomposition of product Overdrying State of subdivision Product temperature h. Bulk density... 

It is essential that the sodamide be very finely divided. The state of subdivision of the sodamide particles seriously affects the yield of product. A mechanical grinder was used by the original authors who obtained better yields than those reported here. 

The chemical reactivity of boron itself obviously depends markedly on the purity, crystallinity, state of subdivision and temperature. Boron reacts with F2 at room temperature and is superficially attacked by O2 but is otherwise inert. At higher temperatures boron reacts directly with all the non-metals except H, Ge, Te and the noble gases. It also reacts readily and directly with almost all metals at elevated temperatures, the few exceptions being the heavier members of groups 11-15 (Ag, Au Cd, Hg Ga, In, Tl Sn, Pb Sb, Bi). 

In terms of the two-phase system which comprises dispersions of solids in liquids, the minimum energy requirement is met if the total interfacial energy of the system has been minimized. If this requirement has been met, chemically, the fine state of subdivision is the most stable state, and the dispersion will thus avoid changing physically with time, except for the tendency to settle manifest by all dispersions whose phases have different densities. A suspension can be stable and yet undergo sedimentation, if a true equilibrium exists at the solid-liquid interface. If sedimentation were to be cited as evidence of instability, no dispersion would fit the requirements except by accident—e.g., if densities of the phases were identical, or if the dispersed particles were sufficiently small to be buoyed up by Brownian movement. 

State of subdivision. The smaller the pieces of a solid reactant—the smaller the state of subdivision—the faster the reaction. Wood shavings burn faster than solid wood, for example, because they have more surface area in contact with the oxygen with which they are combining (for a given mass of wood). In a sense, this is also a corollary of factor 4. 

Mixtures with sulfur are unstable, and may ignite some hours after preparation, depending on the state of subdivision and atmospheric humidity [1], Selenium reacts violently with aqueous solutions of the oxidant [2],... 

Chlorine trifluoride is a hypergolic oxidiser with recognised fuels, and contact with the materials following at ambient or slightly elevated temperatures is violent, ignition often occurring. The state of subdivision may affect the results. 

Reactivity towards air or oxygen increases from lithium to caesium, and the intensity depends on state of subdivision and on presence or absence of moisture. Lithium normally ignites in air above its m.p., while potassium may ignite after exposure to atmosphere, unless it is unusually dry. Rubidium and caesium ignite immediately on exposure [1], It is reported that sodium and potassium may be distilled unchanged under perfectly dried oxygen [2],... 

A state of subdivision of matter with a particle size between 10"7 and 10 5 cm (1 nm to 100 nm). The properties of colloids lie between those of true solutions and coarse suspensions. 

As the state of subdivision of a solid increases, the surface area of the solid available to react becomes greater. Because reactions take place at the surface of a solid, the rate of reaction increases. This explains why solid chemicals are often supplied in powder form rather than in large lumps. 

Cellulose nitrate is very easily ignited and bums very rapidly or explosively, depending on the degree of confinement, degree of nitration and state of subdivision. Unless very pure and stabilised, it deteriorates in storage and may ignite... 

State of subdivision, implying that the molecules or polymolecular particles dispersed in a medium have at least in one direction a dimension roughly between 1 nm and 1 pm, or that in a system discontinuities are found at distances of that order. (Gold Book online, 1972 entry [2].)... 

Most chemical reactions occur in solutions. This is because a substance dissolved in a solvent, the solute, will be in its smallest state of subdivision, existing as individual molecules or ions that will increase their ability to react with other molecules or ions. Most chemistry in the body takes place in solution in the absence of the solution, much of the chemistry of life would not take place. You are familiar with solutions that are liquid, like iced tea and sea water, but solutions can also be gases, like the atmosphere, or solids, like a gold ring, which is a mixture of silver dissolved in gold. 

Inflammability or Flammability (latter is preferred in modern usage). The ease with which a material (gas, liquid or solid) will ignite, either spontaneously (pyrophoric), from exposure to a high-temperature environment (autoignition), or to a spark or open flame. It also involves the rate of spreading of a flame once it has started. The more readily ignition occurs, the more flammable the material less easily ignited materials are said to be combustible, but the line of demarcation is often indefinite, and depends on the state of subdivision of the material as well as on its chemical nature... 

Levigating agents substances that aid in reducing another substance to an extremely fine state of subdivision after that other substance has been made into a paste with some suitable liquid in which it is insoluble also, nonsolid vehicles used to disperse a solid substance to a paste. 

The double melting point has been observed in only one 5 of the previous studies. The initial melting point varies with the state of subdivision and is not a reliable index of purity. Several recrystallizations did not change the melting behavior or the remelt temperature. The checkers did not observe the double melting point with the product initially obtained, but did so with material recrystallized once. 

The temperature at which mercury fulminate explodes depends upon the rate at which it is heated anefr, to some extent, upon the state of subdivision of the sample. Wohler and Matter 11 experi-... 

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